Characterization of PM₂₅ and PM₁₀ in the South Coast Air Basin of Southern California: Part 1-Spatial Variations

In December 1994, the South Coast Air Quality Management District (SCAQMD) initiated a comprehensive program, the PM₁₀ Technical Enhancement Program (PTEP), to characterize fine PM in the South Coast Air Basin (SCAB). A 1-year special particulate monitoring project was conducted from January 1995 to February 1996 as part of the PTEP. Under this enhanced monitoring, HNO₃, NH₃, and speciated PM₁₀ and PM_2.5 concentrations were measured at five stations (Anaheim, downtown Los Angeles, Diamond Bar, Fontana, and Rubidoux) in the SCAB and at one background station at San Nicolas Island. PM_2.5 and PM₁₀ mass and 43 individual species were analyzed for a full chemical speciation of the particle data. The PTEP data indicate that the most abundant chemical components of PM₁₀ and PM₂₅ in the SCAB are NH₄+ (8-9% of PM₁₀ and 14-17% of PM₂₅), NO₃^- (23-26% of PM₁₀ and 28-41% of PM₂₅), SO₄= (6-11% of PM₁₀ and 9-18% of PM_{2 5}), organic carbon (OC) (15-19% of PM₁₀ and 18-26% of PM_2.5), and elemental carbon (EC) (5-8% of PM₁₀ and 8-13% of PM₂₅). On an annual average basis, PM₂₅ comprises 52-59% of the SCAB PM₁₀. Annual average PM₁₀ and PM_2.5 concentrations showed strong spatial variations, low at coastal sites and high at inland sites. Annual average PM₁₀ concentrations varied from 40.8 ug/m³ at Anaheim to 76.8 ug/m³ at Rubidoux, while annual average PM_2.5 concentrations varied from 21.7 ug/m³ at Anaheim to 39.8 ug/m³ at Rubidoux. The chemical characterizations of the PM_2.5 and PM₁₀ concentrations, as well as their spatial variations, were examined; the important findings are summarized in this paper, and the temporal variations are discussed in the companion paper.¹.